The present invention relates to a new and improved construction of gas-blast switch.
In its more specific aspects the invention relates to a new and improved gas-blast switch comprising a stationary contact element and a movable contact element operatively coupled to drive means and surrounded by a blast nozzle conjointly movable therewith. The blast nozzle has an inlet communicating with a pump chamber or space containing an extinguishing gas and pressurizable during a cut-off stroke of the gas-blast switch. The pump chamber or space is enclosed by a pump cylinder conjointly movable with the blast nozzle and is bounded at one of its ends by the blast nozzle and at its opposite or other end by a spring-supported pump piston which is displaceable from an initial or starting position when the pressure rises in the pump space. Operatively associated with the pump piston is a shock absorbing means.
In such type of gas-blast switches as known for example, from U.S. Pat. No. 2,922,010, granted Jan. 19, 1960, the extinguishing gas is displaced from the pump chamber or space through the blast nozzle during a cut-off stroke to blow the switching arc. On the other hand, the switching arc generates high frequency oscillations in the gas flow due to the enormous heating of the extinguishing gas. These oscillations also propagate back to the pump chamber or space at about the velocity of sound in the form of pressure peaks and pressure minima. To alleviate the effects of such pressure oscillations, which are superimposed upon on the ascending pressure of the extinguishing gas in the pump chamber or space during a cut-off stroke, on the mechanical components of the switch which delimit the pump space the pump piston is resiliently supported and shock absorbing means are associated therewith.
In the aforementioned prior art construction of gas-blast switch, however, the pump piston is directly supported at the spring operatively associated therewith as well as directly coupled to the shock absorbing means. Additionally, the shock absorbing means have a decidedly strongly degressive characteristic, i.e., the shock absorbing means are very "rigid" or "hard" during the initial pressure-caused yielding movements of the pump piston. Only when the pump piston is near the end of the cut-off stroke, i.e., when the volume of the pump chamber or space practically has decreased to zero, and such pump piston is positively further displaced by the pump cylinder against the action of the spring, i.e., when the pump piston already has travelled through a certain distance while yielding, does the hydraulically designed shock absorbing means of the known gas-blast switch assumes a "soft" characteristic. Such design, however, does not contribute to alleviating the effects of the aforementioned pressure oscillations, rather is designed with the intent of decreasing the pumping stroke of the pump cylinder relative to the pump piston in comparison to the total switching stroke. In this known construction of gas-blast switch all of the components bounding the pump chamber or space, notwithstanding the provision of the spring support for the pump piston, have to be dimensioned in consideration of the magnitude of the highest possible pressure peaks occurring in the pump chamber or space, and also the drive means for the gas-blast switch have to be correspondingly dimensioned.